U.S. Pat. No. 4,114,841 discloses a method for stabilizing an orbiting satellite utilizing magnetic torquing. The magnetic torque can be developed to change the spin rate of the orbiting satellite only when the earth's presence is detected. This superficially appears to be related to that aspect of the present invention in which the signal 14 produced by attitude sensor 3 is clamped to within the astronomical body detection domain 26 in order to limit the spin velocity of spacecraft 2. However, the cited reference pertains to reducing the spin rate of a spin-stabilized satellite about its spin axis. On the other hand, when the present invention is used with a spin stabilized space vehicle, it is to make stationary the despun portion of the space vehicle with respect to an astronomical body such as the earth, and does not relate to the spinning portion of the space vehicle. Furthermore, the cited reference does not use hysteresis as in the present invention.
Similarly, U.S. Pat. No. 3,749,914 pertains to aligning the spin axis of a spin-stabilized space vehicle with respect to an external reference. As stated above, the present invention, in the embodiment in which it is used for a spin-stabilized space vehicle, operates on the despun portion of the space vehicle, not on the spinning portion.
U.S. Pat. Nos. 4,288,051 and 4,358,076 disclose techniques for acquiring the sun and earth from the vantage point of a spacecraft, which techniques could be used by attitude sensor 3 of the present invention.
U.S. Pat. No. 3,834,653 shows a type of torque controller which could be used as torquing means 25 of the present invention. Also note earth time detectors 42 and 44.
U.S. Pat. No. 4,114,842 is a system for recapturing the altitude (not attitude) of an aircraft; it is not a system for stabilizing the attitude of a spacecraft with respect to an astronomical body as in the present invention.